The AN6581 is a synchronous four-switch bi-direction buck-boost DC/DC controller capable of regulating the VBUS/VBAT voltage at, above, or below the VBAT/VBUS voltage. The AN6581 operates over a wide input voltage range of 3V to 40V to support a variety of applications. The AN6581 employs current-mode control both in buck and boost modes of operation for superior load and line regulation. The switching frequency is programmed by an external resistor. This device also features a programmable soft-start function and offers protection features including cycle-by-cycle current limiting, input undervoltage lockout (UVLO), output overvoltage protection (OVP), and thermal shutdown. The AN6581 is available in an QFN4x4-32L package, provides a very compact system solution and good thermal conductance.